Competitive altruism from reciprocity to the handicap principle

Competitive altruism: from reciprocity to the
handicap principle
Gilbert Roberts
yne,
Evolution and Behaviour Research Group, Department of Psychology, University of Newcastle uponT Newcastle uponTyne
NE1 7RU, UK (gilbert.roberts@ncl.ac.uk)
Current work on cooperation is focused on the theory of reciprocal altruism. However, reciprocity is just
one way of getting a return on an investment in altruism and is di¤cult to apply to many examples. Reci-
procity theory addresses how animals respond dynamically to others so as to cooperate without being
exploited. I discuss how introducing di¡erences in individual generosity together with partner choice into
models of reciprocity can lead to an escalation in altruistic behaviour. Individuals may compete for the
most altruistic partners and non-altruists may become ostracized. I refer to this phenomenon as competi-
tive altruism and propose that it can represent a move away from the dynamic responsiveness of
reciprocity. Altruism may be rewarded in kind, but rewards may be indirectly accrued or may not
involve the return of altruism at all, for example if altruists tend to be chosen as mates. This variety
makes the idea of competitive altruism relevant to behaviours which cannot be explained by reciprocity. I
consider whether altruism might act as a signal of quality, as proposed by the handicap principle. I suggest
that altruistic acts could make particularly e¡ective signals because of the inherent bene¢ts to receivers. I
consider how reciprocity and competitive altruism are related and how they may be distinguished.
Keywords: cooperation; altruism; reciprocity; handicap principle; Prisoner's Dilemma
1. INTRODUCTION 2. THE PROBLEM OF ALTRUISM AND THE SOLUTION
OF RECIPROCITY
Altruistic behaviour fascinates evolutionary biologists
because altruism, by de¢nition, incurs a ¢tness cost. A fundamental problem besetting work on altruism is
Why should an animal perform a costly act ? For unre- the di¤culty in demonstrating the costs and bene¢ts
lated individuals, answers have focused on Trivers' (1971) involved. Consequently, it is di¤cult to draw up a list of
theory of reciprocal altruism. However, the stability of altruistic behaviours requiring explanation, let alone to
reciprocity is problematic because altruists may be actually explain them. Behaviours previously labelled
exploited by individuals which fail to reciprocate. A solu- altruistic (such as predator inspection visits by ¢sh, Mili-
tion to this problem has been developed through nski 1987) have been re-interpreted as involving direct
computer simulations pioneered by Axelrod & Hamilton self-interest (Connor 1996). Nevertheless, it is reasonable
(1981). If animals use responsive strategies such as Tit-for- to develop a theory of when we may expect to ¢nd
Tat, then reciprocity can become established. Y the et altruism, even if the selective bene¢ts of any particular
problem of exploitation will be so pervasive that recipro- behaviour are unclear. Arguably, examples of altruism
city is only likely to become established under restricted include alarm calling, sentinel behaviour, territorial
conditions (Axelrod & Hamilton 1981). In this paper, I defence, allogrooming, allofeeding, cooperative foraging
suggest a shift in focus from how individuals can avoid and restraint in contests (Dugatkin 1997).
exploitation by cheats, to how individuals may compete The theory of reciprocal altruism currently dominates
to develop reputations as the most altruistic. This new discussion of non-kin altruism (see, for example, Brembs
perspective arises from incorporating individual di¡er- 1996). It has been the subject of scores of theoretical
ences together with partner choice. I go on to argue that papers based on the iterated Prisoner's Dilemma game.
altruism may be interpreted as a signal. I draw a parallel In this scenario, mutual cooperation pays well, but
between the di¤culty in explaining altruistic behaviour exploiting a cooperator pays best; mutual refusal to coop-
and the di¤culty in explaining costly displays used in erate pays poorly, but cooperating and being exploited
mate choice. In fact, Zahavi (see, for example, Zahavi pays worst of all. Cooperation appears doomed to failure.
1977) has drawn attention to this parallel, but the However, if players use a Tit-for-Tat strategy (cooperating
handicap principle has not been widely developed as an on the ¢rst move and then playing as the other player did
explanation of altruism, despite its recognition as a on its last move) over repeated interactions then recipro-
widely applicable theory (Grafen 1990). Here, I highlight city can become established (Axelrod & Hamilton 1981).
the possible application of the handicap principle to The key problem is in relating the elegant theory to the
altruism, explore its relation to reciprocity, and examine evidence. As yet, there is little evidence for the theory
how we may test the theories. (see, for example, Wilkinson 1984), though this lack of
Proc. R. Soc. Lond. B (1998) 265, 427^431 427 & 1998 The Royal Society
Received 10 November 1997 Accepted 1 December 1997
428 G. Roberts Competitive altruism
evidence may be consistent with the prediction that reci- the conclusion that it can only be stable within a narrow
procity will only develop in restricted conditions. range of conditions are linked to the way in which models
Nevertheless, there is clear evidence of dissatisfaction with based on the iterated Prisoner's Dilemma have been
the current paradigm based onTit-for-Tat behaviour in an implemented. In the following, I consider the conse-
iterated Prisoner's Dilemma. This is manifested in a claim quences of changing some of the standard assumptions.
that there is no evidence for the paradigm (Clements &
Stephens 1995) and a call for a new paradigm (Brembs
3. INDIVIDUAL DIFFERENCES AND PARTNER CHOICE
1996).
CAN LEAD TO AN ESCALATION OF GENEROSITY
It is not the object of this paper to provide a detailed
critique of work on reciprocity. Rather, it is my aim to ask Imagine that individuals can make a strategic decision
a more fundamental question. Namely, even if the theory about how much of their available resources to invest in
proved essentially sound and even if there were a number altruism. I refer to this as their `generosity'. Imagine also
of uncontroversial examples, could reciprocity provide a that individuals can choose to interact with particular
general explanation for altruistic behaviours among non- other individuals on the basis of their experience and that
kin? Reciprocity is not a catch-all term for eventually they prefer generous partners. There are a number of ways
bene¢ting from altruism: it speci¢cally refers to interac- of implementing the themes of varying generosity and
tions within dyads, whereby a short-term cost paid by partner choice into simulation models. Roberts (1998)
one individual leads it to receive a greater bene¢t from and Sherratt & Roberts (1998) o¡er two di¡erent ways of
another individual. Reciprocity can involve exchange of doing this, based on an explicit consideration of the costs
services which an animal cannot ever perform for itself and bene¢ts involved in reciprocal altruism. We ¢nd that
but which it can perform for others (e.g. impala, Aepyceros in some conditions, simple partner-choice rules can lead
melampus, are unable to groom their necks themselves; to the most generous individuals partnering other
Hart & Hart 1992). Or it can involve exchange of di¡erent generous individuals and leaving non-altruists ostracized.
services at the same or di¡erent times (e.g. trading eggs for This can mean that the most generous also receive the
sperm in simultaneous hermaphrodites, Connor 1992). Or most, and if this feeds back into the number of o¡spring
it can involve provision of a service at one time which is produced, generous strategies can spread. The key result
returned at a later date (e.g. food sharing among vampire is a very simple one: introducing individual di¡erences in
bats, Desmodus rotundus; Wilkinson 1984). Even if recipro- generosity combined with partner choice can lead to
city could o¡er a solution for such cases, many cases do competition for partners and thereby to an escalation in
not ¢t into these categories. It is not clear how reciprocity generosity which is rewarded by greater bene¢ts for those
et
could explain altruism which bene¢ts a group. Y if, for which choose to or can invest more.
example, territorial defence (e.g. among lionesses, Panthera
leo; Heinsohn & Packer 1995) is altruistic, a whole group
4. ALTRUISM WITHOUT DIRECT RECIPROCATION CAN
bene¢ts rather than just one individual reciprocator. It is
BRING BENEFITS THROUGH REPUTATION-
not clear how reciprocity could explain altruism which is
BUILDING
consistently asymmetric or even entirely one-way. Y et
allopreening, for example, is two-way in some species of A natural extension of reciprocity is to consider whether
birds but just one-way in others (Harrison 1965). Humans altruism can bring bene¢ts even if it is not reciprocated
often seem to be more altruistic than would be predicted directly. Can it ever pay an individual A to perform an
on economic grounds (see, for example, Frank 1988). altruistic act for individual B to gain from individual C ?
Furthermore, they are often altruistic to non-reciprocators In other words, can non-reciprocal altruism play a role in
(e.g. by donating to charities). An important theme of this developing partnerships for reciprocal altruism? Many
paper is that reciprocity is just one way of getting a return interactions between organisms occur within partnerships,
on an investment in altruism. Recent work has tended yet partners change. Hence, I suggest that one realistic
towards a classi¢cation of cooperative behaviours as way in which to model interactions may be to have a two-
either mutualistic or reciprocal (see, for example, stage model incorporating both an `assessment' stage and a
Mesterton-Gibbons & Dugatkin 1997) as if these were the `partnered' stage. In the assessment stage, animals interact
only possibilities. Other mechanisms deserve attention. with the whole population, whereas in the subsequent
I start by re-examining some of the assumptions of the paired stage they interact solely with their chosen partner.
current theoretical framework and suggesting a modi¢ed Again, there is a range of ways in which such a scenario
approach. Most computer simulations, such as those of could be modelled, but some general features can be
Axelrod & Hamilton (1981) have been based on indivi- outlined. In the previous section, I considered that indivi-
duals which interact repeatedly with a particular partner duals might di¡er in their generosity. This had direct
or with all others (a round robin tournament). In many bene¢ts through assortative partner choice. However, we
real situations, individuals can choose between potential can also imagine a scenario whereby high generosity does
partners, and those partners may be unequal both in not have such direct bene¢ts. It may be that an increase in
strategy and in the resources which they allocate to generosity in the assessment stage is uneconomic in the
altruism. This is not to say that partner choice (see, for short-term, but that the debt could be recouped in the
example, Bull & Rice 1991; Peck 1993) and varying invest- long-term if the generous altruist was more likely to
ment in altruism (Frean 1993) have not been considered, obtain a generous, pro¢table long-term partner.
nor to say that models which do not include more bio- An alternative scenario is to think of individuals as
logically realistic complications have nothing to o¡er. di¡ering in `forgiveness', where forgiveness represents
However, the focus on the instability of reciprocity and the probability of behaving altruistically towards an
Proc. R. Soc. Lond. B (1998)
Competitive altruism G. Roberts 429
individual which has not reciprocated in the past. Once plausible in small, tight social groups in which individuals
again, if individuals use information about the altruistic will make use of information other than their own experi-
behaviour of others in deciding with whom to form a ences. However, there are also problems in using
long-term partnership, then it may be worth going into information not based on personal experience because
debt in the short term to secure a pro¢table, altruistic how individuals behave with others is not necessarily a
partner in the longer term. good guide to how they will behave with you.
Altruists might recoup their costs in a number of ways.
First, altruism may lead to direct reciprocation, as
5. BEYOND RECIPROCITY: COMPETITIVE ALTRUISM
proposed by Trivers (1971). Second, altruism may not be
A key theme of the above scenarios is that, perhaps reciprocated directly by the recipient, but may bring
paradoxically, competition between unequal individuals indirect economic bene¢ts through more generous or
may be an important driving force in cooperation. This is more forgiving individuals being able to select more coop-
surprising because the Prisoner's Dilemma paradigm sees erative partners for longer-term reciprocal interactions. A
individuals as being better o¡ in the short term by taking potential problem with this scenario is that an individual
the bene¢ts without paying the costs. For example, at any might cheat by securing a reputation and then defecting.
one time, a bird might do best by being allopreened One answer is that this need not be a problem if the repu-
without returning the service. However, I suggest that, in tation is continually tested and individuals can switch
certain circumstances, individuals may compete to be and partners. Another answer to this is that if altruistic beha-
to be seen to be altruistic. viour serves as a signal of individual quality then
This shift in emphasis arises from considering the wider reciprocation need not continue. Altruism might not be
context in which interactions take place. Thus, allopre- maintained by the return of altruism at all, and the
eners may not just be playing with each other, they may altruist may bene¢t not through receiving altruistic acts
be competing against a population of potential partners. either directly or indirectly, but in other ways, such as
Those who allopreen can be thought of as a resource for increasing its mating opportunities. This brings us to the
which others compete. Individuals may still face the essen- handicap principle.
tial problem encapsulated in the Prisoner's Dilemma,
namely that exploitation pays better than cooperation.
6. CAN ALTRUISTIC BEHAVIOUR BE UNDERSTOOD
However, where there is competition for partners, the
AS A HANDICAP?
most altruistic can preferentially interact with each other,
leaving non-altruists ostracized and unable to exploit The peacock's tail has become a metaphor for the
them. Thus, in e¡ect, cheating is not a pro¢table option. apparent over-indulgence of many animals in attributes
The paradox is that to score points in the wider context it used in mate choice. Zahavi has argued that the cost of
may be necessary to forego points in the narrow con¢nes such characters was an essential feature of an honest
of a particular interaction de¢ned by the Prisoner's signalling system (Zahavi 1975). The idea was initially
Dilemma. If reputation is more important than short- controversial but gained credibility with Grafen's (1990)
term gains, then altruism could persist in a Prisoner's models. Grafen (1990) showed through an evolutionarily
Dilemma through competition: competition for the atten- stable strategy (ESS) model how costly, strategic signals
tions of other altruists, competition for mates. If the could provide an honest indicator of quality. Zahavi
competition is for higher stakes than is any particular (Zahavi 1977, 1995; Zahavi & Zahavi 1997) has argued
altruistic interaction, the one who invests more in altruism that altruism can be understood as a handicap. However,
may be at a competitive advantage. while Grafen (1990) recognized the wide applicability of
This is important for two reasons. The ¢rst is that it the handicap principle, the theory has not been widely
predicts that the occurrence and nature of cooperative developed in the ¢eld of altruistic behaviour and a recent
interactions will depend on the extent of individual di¡er- review of cooperative behaviour makes no mention of it
ences and the potential for competition between partners. (Dugatkin 1997).
The second is that behaviour may not be as directly Can altruistic behaviour qualify as a handicap? T o
responsive as has previously been predicted. The link address this question I consider a behaviour which may
between performing an altruistic act and receiving a qualify as both sexually selected and altruistic, namely
bene¢t is likely to become less direct if individuals both allopreening by a male of a female. Advertising can be
use information gained from watching others interacting considered as the level of investment in allopreening. If
and act so as to be observed. There would seem to be a the following hold, then the handicap principle can apply.
bene¢t to individuals which could avoid interacting with Males of higher quality (where quality encompasses attri-
those it has observed to be exploitative, and which could butes such as time and energy available for activities such
encourage cooperative individuals to preferentially as allopreening which do not directly contribute to
interact with them. It is therefore surprising that little survival) have higher ¢tness. A male will be better o¡ if a
attention has been paid to such reputation-based beha- female assesses its quality as being high. Allopreening
viour, Pollock & Dugatkin (1992) being an exception. reduces ¢tness and is more expensive to those of lower
Axelrod (1984) brie£y considers the e¡ects of reputations quality. The gain in ¢tness to a partner from a better
and suggests that it is best to foster a reputation as a bully assessment is at least as great as for an individual with
so that you will be at a lower risk of exploitation. I suggest high reserves as for one with low. Given these assertions,
instead that where there is competition for partners of it follows from Grafen (1990) that we can expect that at
di¡erent quality, a generous reputation could pay o¡ in the ESS, higher quality males will allopreen more, and
the long term. The use of reputations is particularly the costs incurred will be more than compensated for by
Proc. R. Soc. Lond. B (1998)
430 G. Roberts Competitive altruism
the e¡ects on female choice. Thus, an individual might altruism predict a correlation across individuals between
make a strategic investment in altruism which acts as a acts performed and acts received, but in reciprocity this
signal of its ability to be altruistic or of some other aspect derives from the prediction of a Tit-for-Tat, responsive
of its quality, and which in£uences receiver behaviour in strategy whereas in competitive altruism it derives from
such a way that the ¢tness of the altruist is increased. The assortative partner choice. Even if behaviour is still
implication of this argument is that with a few reasonable responsive, it may be more £exible and less dependent on
assumptions we can apply the handicap principle to an the probability of future interactions with a particular
altruistic act and we can use the theory developed for partner. Individuals may perform acts of altruism to
handicap signals in general. However, there is a particu- enhance their reputations, so there may be a looser link
larly interesting feature of altruism as a signal which I between giving and receiving than in direct reciprocity.
will now address. In impala (Hart & Hart 1992), grooming does seem to be
dynamically reciprocal, with virtually every move being
matched. In comparison, allopreening sequences of
7. ALTRUISM AS A SIGNAL BENEFITING THE
breeding pairs and neighbouring guillemots Uria aalge (G.
RECEIVER
Roberts, unpublished data) do not show strict Tit-for-Tat
Perhaps the most unusual feature of altruism as a signal responsiveness. It therefore seems reasonable to accept
is that the receiver actually bene¢ts. This is in contrast to reciprocity as a good explanation in impala, but the
typical signaller ^ receiver interactions where the receiver number of examples of such dynamic responsiveness is
expends energy, time or risk in assessing signals limited.
(Dawkins & Guilford 1991). These authors argued that In allopreening, interactions are often two-way, with
receiver costs will impose a selection pressure away from continual reversal of the roles of altruist and recipient,
honest signalling towards conventional signalling which is but in some species allopreening is just one-way (Harrison
open to cheating. However, if a receiver actually bene¢ts 1965). If we are to explain two-way allopreening as reci-
from an altruistic signal then this argument may not procal altruism then, unless the reciprocation is in a
apply. Altruistic signals may be less likely to become unre- di¡erent currency, we must look for a di¡erent class of
liable through the e¡ects of the receiver costs discussed by explanation for one-way allopreening. An appealing
Dawkins & Guilford (1991). Indeed, there is the intriguing feature of competitive altruism is that it can provide an
possibility that altruism could be used by signallers to explanation for altruism whether or not it is reciprocated.
promote attention to their signals. There is a parallel here Competitive altruists are not necessarily afraid of defec-
with commercial advertising. Some advertisers promote tion because altruism may not be maintained by the
products by o¡ering `free gifts'. This is their way of return of altruism at all. How can altruism be favoured
attracting the reluctant consumer's attention to their without reciprocation? If altruism is a signal, the bene¢ts
products. They o¡er an incentive to attend. If this `free of the altruistic act to the recipient may be largely inci-
gift theory' is correct, mate-choice signals involving dental. The bene¢ts to the altruist may come not through
altruism should be particularly widespread. We can reciprocity, but as a result of in£uencing receiver beha-
expect selection on receivers in favour of attending to viour in some other way. In allogrooming impala and
altruistic signals. Thus, signals are unlikely to be arbitrary. allofeeding vampire bats, the bene¢ts appear to lie very
For example, the most e¡ective way of signalling foraging much in receiving an altruistic act. In these cases, recipro-
ability might be through courtship feeding, which could be city provides a coherent explanation, but such cases seem
seen not as an arbitrary means of strengthening pair to be rare. It is worth considering whether allogrooming
bonds but as a signal with a direct bene¢t. among primates and allopreening among birds may be
maintained by selective bene¢ts other than reciprocation.
In these cases, the altruist may bene¢t through forming
8. DISCUSSION: HOW MAY THE THEORIES BE
alliances and partnerships.
DISTINGUISHED?
Is this just a trade of altruism for mating opportunities?
I have discussed a number of mechanisms which might Consider a bird allopreening its mate or a male o¡ering a
explain the evolution of non-kin altruism, from direct reci- nuptial gift to a female. There is the potential for a
procity among individuals which di¡er in their generosity Prisoner's Dilemma here in that the recipient might
and which can choose partners, through reputation-based defect by receiving the bene¢t and giving nothing in
behaviour, to altruism as a signal of quality. There is a return, whether in the same currency or in terms of
wide range of scenarios in nature and we may need a mating opportunities. However, if the gift is a signal of
corresponding range of explanations. Seeing altruistic quality, then there may not be an incentive to defect by
behaviour as a signal provides a possible link between not mating. If one of the bene¢ts of an altruistic reputation
these mechanisms, but how can we distinguish the is improved mating success then, in practice, altruism may
theories? have as much to do with sexual selection as with the
If altruism is competitive then the conditions in which we economics of reciprocity. The level of altruistic behaviour
should expect to ¢nd altruism and the nature of the found may relate more to the potential for competition
behaviour we ¢nd may di¡er from the predictions of between prospective partners than to the simple
reciprocity. Reciprocity is about dynamically responsive economics of, for example, grooming. Furthermore, for
behaviour, in which altruistic acts are rewarded and reciprocal altruism to result in mutual gain, the bene¢ts
non-altruism punished. Competitive altruism simply pre- to the recipient must be greater than the costs to the
dicts that on average a highly altruistic individual should altruist. However, if altruism is not maintained by recipro-
receive more. Thus, both reciprocity and competitive city, this need not be so. It need only be the case that the
Proc. R. Soc. Lond. B (1998)
Competitive altruism G. Roberts 431
eventual ¢tness bene¢ts to the altruist exceed the costs of helpful discussions and comments. I am supported by a Lord
the altruistic act. Adams Fellowship.
If a whole group gains from an altruistic act, who is to
return the favour? Although there have been attempts to
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